It is known how to process porous refractories made of swellable material in the manner described above (DE-AS No. 11 65 477). For this purpose, the material to be processed and broken up into the desired pellet size, such as clay or oil shale, is placed into chambers arrayed above one another of a shaft, where each chamber is filled partially only, so that a free interspace remains between a pile present in any one chamber, and the bottom of the next higher consisting of segments rotatable about the longitudinal axis, into which free space burning gases produced by burners arranged laterally in the walls of the shaft are introduced. To avoid clumping of the material, a mechanical loosening of the granular material is effected by the bottoms being driven rotarionally, and their being equipped with teeth pointing downwards and reaching into the proximity of the next bottom.
It has further become known DE AS No. 12 43 827 how to arrange burner chambers on both sides of the shaft, and to connect these with the interior of the shaft by means of passages in the wall of the shaft, where the interior of the shaft is again subdivided into chambers by means of bottoms consisting of rotatable segments. By suitable control of the bottom segments of the individual chambers and the use of a feed device sreening the two burner chambers alternately, the material dropping from chamber shall be blown at alternately, set into turbulent motion, and thus a cross flow heating of the material shall be accomplished.
In the known process, only a relatively low utilization of the energy of the burning gases it attained, since in the first case the burning gases are transmitted only to the pertinent chamber bottoms and onto the surfaces of the granular material to be treated facing the interstices, while in the second case the heating of the material occurs practically exclusively during the short time of the free fall of the material from chamber bottom to chamber bottom. This poor utilization of the energy of the burning gases requires of necessity that a multiplicity of chambers arrayed above one another must be provided in the shaft, because the temperature of the heating and burning gases cannot be too high, so as not to initiate the swelling process in the exterior zones before a sufficient heating in the interior of the several material particles has taken place.